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IOWA ACADEMY OP SCIENCE 
meter; at Block Island 10,000 to 15,000. It is evident that the products of com* 
hustion of a large city furnish a vast number of nuclei and in this way supply 
the material necessary for the condensation of moisture. It might be askt why 
is the nucleation of the atmosphere so enormous in the winter time? The 
reason, of course, is that there is very little watery vapor in the air at low 
temperatures for condensation on the nuclei to bring them down. The result 
is that the nuclei gradually accumulate as the weather grows colder and colder, 
reaching a maximum at the winter solstice. 
In his later work Barus carried on a series of experiments to determine 
whether or not the ionized nuclei of the atmosphere at Providence were due to 
local causes. To do this, the air before being admitted into the fog chamber 
was past thru a tubular condenser, one surface of which was charged. In this 
way the charge given up by the ions in a given time for a given quantity of 
air was accurately measured. Dividing this charge by 3.4x10-“, J. J. Thom- 
son’s de.termination of the charge of an electron, gave the number of ions per 
cubic centimeter. From this work Barus concluded, quoting his own words, 
“that the ionization of a given region is independent of artificial local contribu- 
tions, however abundant these may be.” We would infer from this that the 
ionization of the atmosphere results from cosmical rather than local conditions. 
